The invention relates to a method for recording data on a magnetic recording medium wherein,a write amplifier is employed to which data signals are provided and which emits write signals to a magnetic head. The write signals are allocated to data signals. The write signals cause changes of magnetization on a recording medium.
It is already universally known to employ a direct recording method when recording data on magnetic tape. In accordance with the writing method respectively employed, the magnetization on the recording medium directly corresponds to the pattern of the write signals which are in the form of write currents through the magnetic head. In case, for example, the generally known NRZI or GCR method is employed as a recording method, every binary character 1 of the data to be recorded corresponds to a change of the magnetization, and the magnetization is not changed given the binary character 0. In the GCR method, the data to be recorded are additionally coded such that no more than two binary characters 0 appear between two binary characters 1.
In the direct recording method, no high-frequency pre-magnetization signals are employed. The recording process is thus non-linear and the sensitivity in the recording is slight. Moreover, high write currents are required in order to magnetize the recording medium up to its saturation. These high write currents cause modulation signals and a cross-talk to the neighboring tracks given a multi-track recording.
A further disadvantage of the direct recording method is that a relatively low storage density can be achieved on the recording medium in the longitudinal direction, since a shift of the rated points in time of the peaks of the read signals appears. This is generally known under the designation "bit shift". Furthermore, the signal-to-noise ratio is low. The principal reason for the peak shift lies in the asymmetry of the magnetization on the recording medium which results from the respective succession of the binary characters 0 and 1 in the data signal. This occurs since the recording medium is magnetized in both directions up to its saturation, and the remanence in the recording medium is a function of the distances between successive magnetization changes.
The read signals have their maximums at those locations at which the magnetic flux respectively exhibits its greatest slope in the positive direction, and has minimums at those locations at which the magnetic flux respectively comprises its greatest slope in the negative direction. These locations are employed in order to decode the data, the read output signals are normally differentiated, and the zero axis crossings of the differentiated read output signals are identified. The peak shifts consequently correspond to the shifts of the 0 axis crossings. Moreover, the differentiation causes an increase of the noise signals, so that the signal-to-noise ratio is great compared to the magnetization.
When the write-in signals have a high-frequency pre-magnetization signal superimposed on them as is known, for for example, from German OS No. 32 33 489, corresponding to U.S. Pat. No. 4,547,818, incorporated herein by reference, the recording medium is magnetized by pre-magnetization signals with a frequency which is greater than the pass band of the read channel. The magnetization is magnetized up to its saturation.
The high-frequency pre-magnetization signals linearize the recording process and the recording becomes more precise. The recording sensitivity is increased, and this makes it possible to achieve a corresponding magnetization with significantly lower write currents. Fewer modulation signals and a low cross-talk result therefrom as advantages.